[cub]

There's no litmus test you can try that can show someone is gay.

I knew someone who I was sure was gay. He went to gay bars, looked 'gay'. One drunken night I bit the bullet in a gay bar and he revealed he wasn't gay - just liked the bars where he felt safe/relaxed. In fact he didn't have much of a sexuality and was pretty much not interested in either sex.

You seem to be on the right path, good luck.